Spark plug



May 27, 1930. P. K. DEVERS SPARK PLUG Original Filed Oct. 22. 1922 Fig.2.

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Patented May 27 1930 UNITED STATES PATENT OFFICE PHILIP K. DEVERS,

OI LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK SPARK PLUG Continuation in part of application Serial No. 596,197, filed October 22, 1922. This application filed January 14, 1926.

This application is a continuation in part of my prior application filed October 22, 1922, Serial No. 596,197. i

The present invention comprises an improvement in spark plugs for internal combustion engines and relates particularly to spark plugs containing silica insulation.

Various attempts and suggestions have been made to utilizerefractory glasses in place of porcelain in the manufacture of spark plugs. These attempts in some instances have depended on the provision in the spark plugs of metal members having the same coefficient of thermal expansion and contraction as the refractory'glass. It also has been suggested to mold the refractory glass while plastic into the structural form desired in the finished article. The low thermal coelficient of expansion-of silica and its highly refractory nature renders practical execution of both these suggestions dificult.

.lln accordance with my present invention, 1 have provided an improved spark plug in which a tube of fused quarts, (or silica),- or other suitable refractory material, is held under compression by a metal member having a different coeficient of thermal expansion and contraction than said refractory material, this member constituting a terminal to which electric connection is made.

In the accompanying drawing, Fig. l illustrates the preparatory stage of the insulating silica member in my new spark plug; Fig. 2 illustrates an intermediate stage of manufacture; Fig. 3 is a longitudinal section of the finished spark plug and Fig. l is a longitudinal section of a modification.

Referring to the drawing, and particularly to Fig. 1, my invention is carried out by first providing a hollow member 1 of vitreous silica, or fused quartz as it is commonly called, with a thin coating 2 of nickel, silver or other metal which is suited for deposition by a process carried out in the cold, that is,--at ordinary temperatures, and which does not have a melting point materially lower than the shell which is set from a fused state about the silica member. Preferably the coating metal should be chosen to alloy with the shell which i Cast about it although this is not Serial No. 81,344.

essential. It is also convenient to choose a metal for coating the quartz which can be convenientl deposited by an electrolytic process. Nickel satisfies all these conditions. Conveniently the outer surface of the silica tube may be first provided with a very thin coating of silver by the well-known chemical reduction process using a solution of silver nitrate, ammonium hydroxide and a weak reducing liquid such as sodium or potassium tartrate. A thin layer of nickel may be deposited electrically upon the silver. In the drawing the coating 2 has been shown somewhat exaggerated in thickness. The coated. tube is then plunged into a body 3 of molten copper contained within a suitable receptacle 4 thereby causing some of the copper to solid ify upon the outside of the tube. The copper will adhere to the thin metal member and to some extent alloy with it. Instead of copper, a cupreous alloy such as bronze or brass or other suitable casting metal may be used, the cupreous alloys being preferred, because of the ease with which they may be worked and because of the fact that they have a marked coeficient of expansion so that when the outer layer of metal is cooled the silica tube will be held under compression. The tube may be dipped repeatedly into the copper until an outer layer of copper of suficient thickness has been applied. Preferably cupreous metal is not allowed to enter the bore 5 of the tube andfor this purpose a plug 6 of graphite or the like is inserted in the lower end of the bore as indicated in Fig. l. l prefer to use fused quartz which is substantially clear for the purpose of my invention as the light from a spark when the spark plug is in use in a combustion motor will be transmitted by the quartz, and thus readily indicate the condition of ignition in the motor.

Fig. 2 shows the article produced by the process above described, the outer shell of copper 7 being shown with the outer surface trimmed to regular shape. (The layer 2 has not been shown.) In the next step of manufacture the shell 7 may be screw-threaded as indicated at 8 in Fig. 3, the upper part being trimmed away from the quartz tube 1 as indicated. This outer shell 8 as usual c n:

stitutes one pole of the electric circuit, a spark point 9 being conveniently mounted upon the shell 7; The opposite pole is constituted by rod 10 having a. diameter less than the bore of the silica tube 1 and being provided at the end with an enlargement 11 which is shaped, by grinding or otherwise, to make a close fit with the lower end of the tube 1 so that when the rod is thrown firmly against the mouth of the tube by a nut 12 it engages with the screw-threaded end of the rod 10 and-thus a tight closure will be produced. Suitable washers 13 and 14: may be provided to hold the parts secure. A spark point 15 may be provided upon the end of the rod 10 as indicated. The construction shown in Fig. 4: is similar to that shown in Fig. 3, except that the quartz member 16 is tapered and the shell 1.7 projects beyond the end of the quartz memher, the other parts being the same.

The taper of the quartz member insures a tight fit when the plug is used in the cylinclers of engines employing extremely high gas pressures, as for example, aeroplane motors.

lNhat I claim as new and desire to secure by Letters Patent of the United States, is:

1. A spark plug for internal combustion engines comprising a tubular member of vitreous silica, a coating of nickel thereon, a shell of oupreous metal superimposed on said nickel and surrounding said tubular member, a conductor having a diameter somewhat less than the bore of said member and passing through said bore, means for sealing said bore and spark points mounted on said conductor and said shell.

2. A spark plug comprising a hollow silica body, a conductor passing through the bore thereof, a relatively thin coat of metal on substantially the entire outer surface of said hollow body and a relatively heavy metal shell alloyed with said thin coating, and spark points mounted on said conductor and shell.

8. A spark plug comprising a hollow silica body, a conductor passing through the bore thereof, a relatively thin coat of metal on the outer surface of said hollow body and a relatively thick metal layer alloyed with and contacting throughout substantially its entire length with said coating, and spark points connected to said conductor and layer.

In witness whereof, I have hereunto set my hand this 12th day of January, 1926.

PHILIP K. DEVERS. 

